1. Field of the Invention:
Particularly, the present invention relates to a device capable of projecting an image, a frame of which is made variable on the screen depending on an aspect ratio of the image to be displayed.
2. Description of the Related Art:
FIG. 1 shows a construction of an image projector disclosed in the U.S. patent application Ser. No. 913,445. The image projector shown in FIG. 1 is constituted mainly with a spatial light modulator 1 for forming a red image, a spatial light modulator 2 for forming a green image, a spatial light modulator 3 for forming a blue image, a color combining optical system 4, a first lens group 5, a second lens group 6, a third lens group 7 and a screen 8.
In the reproduction of image by this prior art display device, a reading light from a light source which is not shown is separated through a polarizing beam splitter and dichroic mirrors, etc., to monochromatic red, green and blue lights and supplied to the respective spatial light modulators 1, 2 and 3. Then, images formed on the respective spatial light modulators 1, 2 and 3 are directed to the color combining optical system 4 and combined thereby and the combined image is focused through the first lens group 5 on the second lens group 6. The focused image on the second lens group 6, is passed to the third lens group 7 through which it is projected onto the screen 8 as an image of a predetermined magnifying power.
According to this image projector, it is possible to make a back focal length larger to thereby minimize the thickness or depth of image projector and to obtain an image of high resolution.
It has been known that, with the use of such spatial light modulators of image (light) writing type, it is possible to wright an input image while arbitrarily varying its frame size, configuration or aspect ratio of writing image according to the original form of the input image.
However, since reading light from a light source irradiates uniformly and fully an effective area (area available for writing in or reading out) inherent to the spatial light modulator, unnecessary areas outside the formed image on the spatial light modulator are also irradiated by the reading light resulting in too bright presentation of such unnecessary areas on the screen, this deficiency is aggravated by the reading light reflected from a substrate surface of each spatial light modulator and reaching to the screen so that a frame or fringe of the projected image becomes unclear.
In such a case, it is conceivable that a contrast of an image area to a periphery thereof may be improved by cutting unnecessary light by means of an aperture member composed of a light shielding plate having a predetermined aperture formed therein.
When such aperture member is provided as a fixed structure, there is a problem that it can not respond to an input image whose frame is, for example, larger than a size of the predetermined aperture, resulting in that even necessary area of the image is cut off.